1. Technical Field
In a first context, this document relates to orthopedic devices and methods for their use. For example, this document relates to novel bone drills for performing osteotomies or for drilling holes in bones. The bone drills have at least some centers of mass that are offset from the drill's axis of rotation. Accordingly, the bone drills may rotate and cut using a precessional pattern of motion. In a second context, this document relates to precessional-motion drilling tools generally. For example, this document relates to drill bits and methods of use for drilling a variety of materials including, but not limited to, metals, ceramics, wood, plasterboard, plastics, stone, composites, synthetics, silicon, and the like. This document also relates to dental drills and methods for their use.
2. Background Information
Osteotomies are routinely performed for surgical access or to divide or reposition a bone for surgical correction. Holes may be drilled in bones for various reasons, such as to accommodate screws, pins, dental implants and various other implantable devices and materials, or to collect a bone sample for biopsy. A common example of the need for an osteotomy is a dental implant procedure 10 as depicted in FIG. 1. In this procedure, the surgeon must create a space of a specific diameter and depth in bone 15 (shown in cross-section) to accommodate an implant 20 of corresponding size within the bone 15 and extending above the gum tissue 18. Frequently, the implant is placed sub-periosteally, and autograft bone is used to supplement and aid healing.
The traditional instruments used to create osteotomies resemble ordinary twist drills. These designs were described as early as Hartshorn (1882), and modified by Hanson (1904), Kallio (1960), Kim, (1980) and others. There have been only a few improvements in this technology since that time. Davis (U.S. Pat. No. 5,190,548, May 1993) described a four-sided hollow drill capable of evacuating bone via the tunneled or hollow portion of the drill. Leppelmeier (U.S. Pat. No. 6,312,432, November 2001) described a bone drill, also similar to a twist drill, with a stabilizing point or tip designed to prevent the bone drill from deviating from the long axis of the osteotomy. Leppelmeier (U.S. Publication No. 2012/0004661, January 2012) also proposed an orthopedic drill with flutes having variable helical angles. Lehenkari (U.S. Pub. No. 2012/20245586, September 2012 and U.S. Pub. No. 2013/0110112, May 2013) proposed the use of super-elastic alloys to craft a drill that was multi-directional.
In addition to the minimal improvements in drill technology, these designs offer little opportunity to collect bone for an autograft, which is often necessary. In these cases, the surgeon may use an autograft from another site or he may elect to use allografts or artificial material. Autologous grafts, however, are preferable because they are inherently biocompatible, osteo-conductive, osteo-inductive, and osteogenic. Harvesting autologous bone from a donor site results in additional time and the attendant risk of complications such as donor site pain and morbidity. Allografts, derived from donor (cadaver) tissues, are only osteo-conductive, and may pose the risk of contamination. Artificial materials such as alloplastic bone cement are a poor choice for grafting since they are potentially antigenic and rarely osteo-conductive. Thus, bone collection from the original operating area is desirable.
Performing osteotomies can be challenging even with optimal illumination, magnification and good assistance. For example, in some cases the surgical site may be obscured by blood and bone chips. Keeping the operative field clear during surgery is beneficial. Thus, constant and controlled irrigation with a physiologic media is generally an integral part of these procedures. It is also advantageous to the mechanics of bone cutting, since the flutes of the drills cut more efficiently when the substrate is cooler and in the absence of bone fragments which can clog and stall the drill. Irrigation not only improves the efficiency of the cutting instrument, it also prevents thermal necrosis of the bone which can later retard or negate the healing process. Controlled irrigation takes on even greater importance if the operator intends to capture the bone fragments for reuse in an autograft.
While the use of irrigation is advantageous, delivery of the irrigant to the surgical site typically requires pressurization of the irrigant that can make recovery of bone fragments for an autograft difficult or impossible. An improved method of scavenging bone fragments will permit irrigation under pressure, and aide the surgeon by keeping the operating area cleaner, more visible and more accessible.
Ideally, bone harvesting should be done while performing the osteotomy and still provide adequate access to the surgical for irrigation, while maintaining a clear operating for the surgery.
Previous designs for bone harvesting, such as those suggested by Meller (U.S. Pat. No. 7,033,359) are complex devices comprising a spring, a spring holder arranged around a shank, which is attached to a fixed collection apparatus. The apparatus requires fixation to the head or arm of the handpiece by a retaining pin. The apparatus is essentially intended for bone harvesting and is not designed to prepare the osteotomy for the implant and harvest bone simultaneously. Because the apparatus is solid and fixed, it would also block the irrigant and cause potential over heating of the bony substrate and the bone particles being harvested.
FIGS. 2A and 2B show a conventional bone drill 200. The bone drill 200 shown includes a shaft 202 with a free end or tip 204 and a shank 206. The shaft 202 defines grooves 208 and 210 that spiral around the shaft 202. The grooves 208 and 210 are also referred to in the instant specification as flutes 208 and 210.
FIG. 2B shows a cross-section 212 (i.e., cross-section A-A) of the bone drill 200. The cross-section 208 shows cross-sectional spaces 214 and 216 of the flutes 208 and 210, respectively. The flutes 208 and 210 are generally the spaces on both sides of a helical structure 218 (or helix) that spirals around the shaft 202. The bottom portion of a flute—seen as a line or curve (e.g., curve 220 of FIG. 2B)—is referred to in the instant specification as a spline. The portion of a spline that comes into contact with a surface being cut during cutting will be referred to in the instant specification as a radial land. Item 222 of FIG. 2B is an example of a radial land. A flute of a bone drill usually includes a sharpened edge configured for cutting. Edge 224 of FIG. 2A is an example of such a cutting edge. Edge 224 can be seen as a point 226 in FIG. 2B. Generally, an instrument having right handed cutting edges is one that will cut or remove material when rotated clockwise, as viewed from shank to tip. In this specification, a direction of rotation will be specified as viewed from the shank to the tip of the instrument. The cut direction of rotation for a right handed bone drill is clockwise. An instrument having left handed cutting edges is one that will cut or remove material when rotated counter clockwise. The cut direction of rotation, in this case, is counter clockwise. A bone drill includes a working portion or drill body, which is the portion that can cut or remove material. The working portion is typically the portion along the shaft that is between the tip of the instrument and the shank end of the flutes. Portion 228 is the working portion for the bone drill shown in FIG. 1A. The working portion is also referred to in this specification as the cutting portion, working body, or the drill body; and the working length as the cutting length, or working length.